2009 Climate Statistics for San Juan, PR

Preliminary - Official data will be available from NCDC by mid-2010


2009 Highlights:

  • 4th Warmest year on record in San Juan, PR (warmest average low temperature on record)
  • Warmest October, 2nd warmest December, 3rd warmest July
  • 12th Wettest year in San Juan, PR (2nd wettest June, 3rd wettest November, 3rd driest December)
  • Record number of low temperatures 80 degrees or above (59 days - previous record 32 days)
  • The low temperature of 82 on July 16th, 2009 was tied for the second warmest low temperature ever recorded in San Juan, PR
  • The high temperature of 95 on August 26th, 2009 set a record high temperature for the date and was tied for the warmest temperature of the decade
  • The high temperatue of 78 on February 19th, 2009 was the coolest high temperature ever recorded for the date and the only day in 2009 that the temperature did not reach 80 degrees in San Juan, PR 


Figure 1 - The distribution of temperatures, with respect to the 30-year average, in San Juan, PR


Figure 1 shows the distribution of both low and high temperatures, with respect to the 30-year average in San Juan, PR. For the year, temperatures at the Luis Muñoz Marin International Airport were approximately 1.55F warmer than the 30-year average from NCDC.  The average temperature was below normal only 5% of the days in 2009, while near normal temperatures were observed 34% of the time and above normal temperatures on 61% of the days (near normal was defined as being within 1 degree of the average daily temperature for the date).


As of December 25th, 2009, island wide precipitation was 97% of normal for the year. Due to a very heavy rainfall event Christmas Eve and Christmas Day over the eastern third of the island, year end statistics are expected to be very near normal island wide when all the COOP data is received. A plot of the weekly precipitation and accumulative deviation from normal is displayed in Figure 2.

Figure 2 - Island wide precipitation through December 25, 2009 for the more than 50 cooperative stations

Month by Month Weather Recap:

* January marks the beginning of the dry season across Puerto Rico. However, 2009 began with the remnants of multiple cold fronts brushing the northern half of Puerto Rico, which contributed to above normal precipitation across much of the island for the month.
*The dry season across the local islands generally continues through March. However, at the Luis Muñoz Marin International Airport in San Juan, both February and March 2009 recorded precipitation totals more than one inch above average.
*April generally marks the transition into the rainy season across the local islands. Statistically speaking the month of April is much wetter than March, however this is not always the case. April 2009 was the first full month of 2009 in which below normal precipitation was recorded island wide across Puerto Rico. (An official total of only 2.79" of rain was recorded at the LMM Airport in San Juan, making it the third driest month of 2009.)
*May 2009 was a rather wet month across the local islands due to a fairly persistent area of upper level troughiness that dominated the southwestern Atlantic and much of the Eastern Caribbean Sea. This brought a humid trade wind flow across Puerto Rico, resulting in 26 days in which at least a Trace of precipitation was recorded in San Juan.
*June is normally marked by a short dry spell before hurricane season kicks into full gear locally by the end of July. This was not the case in 2009. The deep and persistent upper level trough that dominated the local region during the month of May, continued over the Southwestern Atlantic and Eastern Caribbean for much of June, promoting a constant flow of moist tropical air over the region. When the month came to a close, June 2009 ended as the second wettest June on record at the LMM Airport in San Juan.
*Precipitation for the month of July was dictated by the typical mesoscale-driven nocturnal/diurnal regime across the local islands. In terms of temperature, July 2009 was one of the warmest on record. A new record for the warmest minimum temperature was set on July 16th, when the morning low temperature only fell to only a balmy 82 degrees. In fact, the low temperature did not fall below 80 degrees a record 19 times during the month!
*At the LMM International Airport, 8.57" of rain fell during the month of August, making it the third wettest month of 2009. To put this in perspective, LMM Airport received 3.35" of rain above the normal value for the month.
*September 10th marks the peak of the hurricane season across Puerto Rico. September 2009 was a rather quiet month tropically speaking, with only two named storms, Erika and Fred. On September 3rd, a tropical storm warning was issued for Puerto Rico and the U.S. Virgin Islands due to the forecast proximity of Tropical Storm Erika.
*October 2009 ended as the warmest October on record at the LMM Airport in San Juan. The average low temperature was 79F, a full degree warmer than the previous record of 78F set in 1980. During the month, the record warmest minimum temperature was tied or broken on 15 separate days, and the average daily temperature was above normal every single day of the month.   
*November 2009 ended as the third wettest November on record and the wettest month of 2009 at LMM Airport in San Juan. The end of November also marked the end of the hurricane season, with below normal tropical cyclone activity observed across the Atlantic basin for the year. A total of nine named storms were observed in 2009, three of which became hurricanes and two of which became major hurricanes.
*December 2009 was the driest month of the year at the LMM Airport in San Juan and 3rd driest December on record. A total of only 1.83” fell over the course of the month, which was 2.54” below the normal of 4.57” for December. 

(Click here for the access to individual monthly reports for 2009)



Summary of 2009 Statistics including the USVI:


Maximum Temperature
Minimum Temperature

San Juan, PR

(Departure from Normal)








Saint Thomas, USVI

(Departure from Normal)








Saint Croix, USVI

(Departure from Normal)








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